In recent years, memory cards having a rewritable, nonvolatile memory medium are becoming widespread. With increased capacity of memory media and a higher recording and reproduction rate, memory cards have now begun to be used for recording video and audio with use of a camera recorder and so on that takes images. With the use of such memory cards, recording apparatuses such as camera recorders that record and reproduce video and audio require a fewer number of mechanically movable parts, which used to be the essential components in conventional tape media and disk media. As a result, it is possible to provide recording apparatuses that are small, light, and less subject to mechanical damage.
Video and audio data recorded on a memory card are generally managed as files by a file system. The file system manages the size of each file, the date and time of updating the record of each file, and the use status and the availability of recording areas such as clusters and sectors. The file system records such pieces of information on a recording medium as management information, together with video and audio files. During capturing of video and audio, the management information is frequently updated as the sizes of the video and audio files gradually increase. It is to be noted that the management information managed by the file system is described as file management information.
Updated data of the file management information is very small compared to the video and audio data recorded. In general, it is known that frequent update of small data in a nonvolatile memory medium such as a flash memory causes such problems as gradual shortening of the rewritable life of the memory medium, that is, reduction in the number of times rewrite is possible, and increased processing time required for updating small data.
In particular, as a result of recent increase in the capacity of flash memories and the like, the size of a collectively-deletable block tends to be larger. Further, when data recorded once is to be partially updated in a size smaller than the block size, the following processing is necessary: reading out the entire block including the part to be updated; replacing only the data of the updating part in the entire block; and writing back the entire block. As a result, the time required for updating the small data tends to increase as the block size expands.
In order to solve these problems, both Patent References 1 and 2, for example, disclose providing one memory card with two types of nonvolatile memory media (recording areas) having different characteristics, and recording file management information in one type of memory medium which is suitable for updating small data.
FIGS. 1A and 1B show an example of conventional formatting of a memory card including a first recording area and a second recording area having different characteristics, and an example of a conventional directory structure of such a memory card.
As shown in FIG. 1A, a memory card 700 includes a first recording area 710 and a second recording area 720. As for the first recording area 710, a memory medium or a memory control method suitable for updating small data is used. In other words, the first recording area 710 allows update of small data in a shorter time than the second recording area 720. The first recording area 710 and the second recording area 720 are assigned consecutive addresses. The first recording area 710 and the second recording area 720 can be seen as a single memory card from outside.
Next is a description of the case where a File Allocation Tables (FAT) file system, which is an example of the file system, manages data recorded on the memory card 700. It is to be noted that the file management information in the FAT file system is described in Patent Reference 3.
As shown in FIG. 1A, a FAT table 730, which is the file management information of the FAT file system, is placed in the first recording area 710. In the case of the FAT file system, the area of the memory card 700 in which files and directories are recorded is divided into many clusters 740, each of which is a unit for managing the recording areas. The clusters 740 are sequentially assigned a cluster number starting from 2.
FIG. 1B shows an example of a directory structure in the FAT file system. For example, as shown in FIG. 1B, a root directory 750 is at the top of the directory structure, and an AV directory 760 is below the root directory 750. A cluster having a cluster number 2 is allocated to the root directory 750, and a cluster having a cluster number 3 is allocated to the AV directory 760. Recorded in these clusters 740 are file management information such as directory entry information which are mainly related to a file stored in the directory and a lower directory.
In such a manner, according to the formatting of the memory card in the conventional example, the FAT table 730 and the directory entry information, which are the file management information of the FAT file system, are placed in the first recording area 710. Since the first recording area 710 is a memory medium suitable for updating small data, such file management information can be updated in a short time.
Further, Patent Reference 3 discloses calculating: the maximum number of files which can be created in the recording medium; and the number of clusters which can store the directory entry information corresponding to the maximum number of files, so as to reserve plural clusters in advance.    Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2006-40168    Patent Reference 2: Japanese Unexamined Patent Application Publication No. 2005-92677    Patent Reference 3: Japanese Unexamined Patent Application Publication No. 2006-252096